JP2008170601A - Image forming method and image forming apparatus using liquid developer - Google Patents

Abstract

An object of the present invention is to provide an image forming apparatus and an image forming method using a liquid developer capable of maintaining a constant state of toner compression with a simple configuration and obtaining a high quality image.
In an image forming method using a liquid developer, a liquid developer in which toner particles comprising a colorant and a resin are dispersed in a carrier liquid, and the toner particles are dispersed in a toner carrier liquid. , A developing roller to which a liquid developer quantified by a toner supply roller and a regulating blade is transferred, a compression member disposed opposite to the developing roller, and a photosensitive member for developing an electrostatic latent image by the developing roller. The compression member has a function of applying an electric field to the liquid developer on the developing roller to compress the solid content toward the developing roller, and the developing roller when a predetermined image is formed and the developing roller The developing current flowing through the photosensitive member is measured, and the strength of the electric field applied to the compression member is controlled so that the measurement result becomes a specified value.
[Selection] Figure 4

Description

  The present invention relates to an image forming method and an image forming apparatus using a liquid developer in which toner particles composed of a colorant and a resin are dispersed in a carrier liquid using a dispersant.

As a prior art of an image forming method using a liquid developer, Japanese Patent Application Laid-Open No. 2002-278291 discloses an image forming method in which a latent image on a photoconductor is developed by a developing roller carrying a liquid developer. A roller-type compression member that contacts the developing roller is arranged as a compression member for compressing the liquid developer of the developing roller, and an independent voltage is applied to the developing roller and the compressing member, respectively. An image forming apparatus is disclosed in which a high-quality image is obtained by preventing the image fogging and density unevenness by applying the voltage applied to the developing roller. Japanese Patent Laid-Open No. 2001-324876 discloses an image forming method using a conductive blade that contacts a developing roller as a compression member.
JP 2002-278291 A JP 2001-324876 A

  A conventional image forming method uses a liquid developer in which toner particles composed of at least a colorant and a resin are dispersed in a non-volatile carrier liquid using a dispersant, and a voltage different from that of the developing roller is applied to a compression member facing the developing roller. This is applied to apply an electric field to the liquid developer to compress the toner particles toward the developing roller to form a film, and the toner particles are easily moved by the electric field in the subsequent development / transfer process. As a result, high development / transfer efficiency can be realized, and a high-quality image without disturbance can be obtained.

  However, in the conventional image forming method, a good film formation state cannot be obtained as the operation of the apparatus continues, and the development / transfer efficiency may change or the image may be disturbed.

  Regarding such a change in film formation state, it is considered that the compression state fluctuates due to a change in characteristics between lots of the liquid developer and a change in charging property and movement characteristic of the liquid developer due to a change with time. Further, the change in the film state of the liquid developer may be influenced by the change in the developing roller resistance with time or the change in the state of the compression member. That is, when using a compression member that is in contact with the developing roller, such as those disclosed in Japanese Patent Application Laid-Open Nos. 2002-278291 and 2001-324876, a change in effective voltage due to a change in the electrical resistance value of the member. Is predicted. In addition, when a compression member using corona or micro discharge is used, a change in the discharge state due to the temperature and humidity environment is expected when an electric field is formed by applying an electric charge to the toner. These fluctuations may cause fluctuations in the compressed state of the toner. Changes in the compressed state of the toner may include changes in image density, disturbance of vertical stripes called ribs, and fogging on non-image areas. Cause a malfunction.

  An object of the present invention is to provide an image forming method and an image forming apparatus using a liquid developer that can solve the above-described problems and can maintain a constant compressed state of toner with a simple configuration and obtain a high-quality image. Objective.

  In order to solve the above problems, the first invention uses a liquid developer in which toner particles are dispersed in a carrier liquid in an image forming method using a liquid developer, and is quantified by a toner supply roller and a regulating blade. A developing roller to which the liquid developer is transferred, a compression member disposed opposite to the developing roller, and a photosensitive member on which an electrostatic latent image is developed by the developing roller, and the compression member is disposed on the developing roller. The developer has a function of applying an electric field to the liquid developer to compress the solid content toward the developing roller, and measures the developing current flowing through the developing roller and the photoconductor when a predetermined image is formed. The strength of the electric field applied to the compression member is controlled so as to be a specified value.

  According to a second aspect of the present invention, in the image forming method using the liquid developer according to the first aspect, the predetermined image is a solid image.

  According to a third aspect of the present invention, in the image forming method using the liquid developer of the first or second aspect, the compression member is a contact roller type, a non-contact roller type, a type using corona discharge, or a contact type. It is one of the types using the conductive blade.

  According to a fourth aspect of the present invention, in the image forming method using the liquid developer according to any one of the first to third aspects of the invention, in color image formation, the predetermined value of the developing current is provided for each of a plurality of colors. To do.

  According to a fifth aspect of the present invention, in the image forming method using the liquid developer according to any one of the first to fourth aspects, the development bias voltage is controlled at a constant voltage.

  According to a sixth aspect of the present invention, in the image forming method using the liquid developer according to any one of the first to fifth aspects, when the liquid developer is recovered and reused, the solid content concentration in the liquid developer It is characterized by comprising a density adjusting means for adjusting the image constant.

  According to the seventh aspect of the present invention, in an image forming apparatus using a liquid developer, a liquid developer in which toner particles are dispersed in a carrier liquid is used, and the liquid developer quantified by a toner supply roller and a regulating blade is transferred. A developing roller; a compression member disposed opposite to the developing roller; and a photosensitive member on which an electrostatic latent image is developed by the developing roller. The compression member applies an electric field to the liquid developer on the developing roller. And has a function of compressing the solid content toward the developing roller, and includes means for measuring the developing current flowing through the developing roller and the photosensitive member when a predetermined image is formed, and the measurement result becomes a specified value. As described above, it comprises control means for controlling the strength of the electric field applied to the compression member.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a main configuration of an image forming apparatus according to the present invention.

  The intermediate transfer belt 70 is an endless belt stretched around a belt driving roller 82 and a driven roller 85, and is rotationally driven while being in contact with the photoreceptors 20Y, 20M, 20C, and 20K. Four primary transfer units 60Y, 60M, 60C, and 60K including the intermediate transfer belt 70, the primary transfer backup rollers 61Y, 61M, 61C, and 61K and the photoconductors 20Y, 20M, 20C, and 20K are arranged on the intermediate transfer belt 70. The color liquid developer is sequentially superimposed and transferred to form a full color liquid developer image.

  The secondary transfer unit 80 includes a secondary transfer roller 81, an intermediate transfer belt driving roller 82, a secondary transfer roller blade 83, and a secondary transfer roller cleaning liquid recovery unit 84, and is formed on the intermediate transfer belt 70. The liquid developer image or the full color liquid developer image is transferred to a recording medium such as paper.

  A fixing unit (not shown) is a device for fusing a single color liquid developer image or a full color liquid developer image transferred onto a recording medium onto the recording medium to form a permanent image.

  The developing units 50Y, 50M, 50C, and 50K develop the latent image with a yellow (Y) liquid developer, a magenta (M) liquid developer, a cyan (C) liquid developer, and a black (K) liquid developer, respectively. It has a function.

  The developing units 50Y, 50M, 50C, and 50K supply the developing toner containers 53Y, 53M, 53C, and 53K that store the liquid developers, and supply the liquid developers from the developing toner containers to the developing rollers 54Y, 54M, 54C, and 54K. Toner supply rollers 51Y, 51M, 51C, 51K, photoconductors 20Y, 20M, 20C, 20K charging units 30Y, 30M, 30C, 30K, and exposure unit 40Y for forming an electrostatic latent image on the charged photoconductor , 40M, 40C, 40K.

  Since the developing units 50Y, 50M, 50C, and 50K have the same configuration, the developing unit 50K will be described below.

  As shown in FIG. 1, a charging unit 30K, an exposure unit 40K, and a primary transfer unit 60K are mainly arranged along the rotation direction of the photoconductor 20K. The photoconductor 20K includes a cylindrical base material and a photosensitive layer formed on the outer peripheral surface thereof, and can rotate around a central axis. In the present embodiment, the photoconductor 20K rotates clockwise.

  The charging unit 30K is a device for charging the photoconductor 20K. The exposure unit 40K has a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and irradiates the modulated laser onto the charged photoconductor 20K to form a latent image. An organic EL head may be used for the exposure unit 40K.

  The developing unit 50K is a device for developing the latent image formed on the photoreceptor 20K using a black (K) liquid developer. The developing unit 50K will be described later.

  The primary transfer unit 60K is a device for transferring the black liquid developer image formed on the photoreceptor 20K to the intermediate transfer belt 70.

  FIG. 2 is a cross-sectional view showing main components of the developing unit 50K. The developing toner container 53K contains a black liquid developer for developing the latent image formed on the photoreceptor 20K. The liquid developer used in this embodiment is a solid particle having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a thermoplastic resin in a liquid solvent such as an organic solvent, silicon oil, mineral oil, or edible oil. It is a liquid developer that is added with a dispersant and has a high viscosity (about 30 to 10000 mPa · s) with a toner solid content concentration of about 25% and is non-volatile at room temperature. A liquid developer whose density is adjusted is supplied from the toner adjusting tank 90K to the developing toner container 53K through a communication pipe 91K provided with a pump. Toner adjustment tank 90K is supplied with toner (solid content concentration 35%) from toner tank 93K through toner supply pipe 94K. Since the toner has high viscosity and low fluidity, it is supplied by a pump. The carrier liquid is supplied from the carrier tank 95K to the toner adjustment tank 90K through a carrier supply pipe 96K provided with an opening / closing valve. Since the carrier liquid has a low viscosity, it is supplied by gravity drop without using a pump. The recovered liquid developer is supplied to the toner adjustment tank 90K through a recovered liquid developer tube 92K from a developing roller cleaning liquid recovery unit 59K described later. A stirring member 97K is disposed in the toner adjustment tank 90K.

  A constant concentration of liquid developer is supplied from the developing toner container 53K to the developing roller 54K by the toner supply roller 51K. The toner supply roller 51K is a cylindrical member and rotates clockwise as shown in FIG. The toner supply roller 51K is an anilox roller having a fine and uniform spiral groove formed on the surface. The groove dimensions are such that the groove pitch is about 130 μm and the groove depth is about 30 μm. A voltage equal to or higher than that of the developing roller 54K is applied to the toner supply roller 51K. The liquid developer quantified by the anilox roller is transferred to the developing roller 54K, and the amount of liquid developer on the developing roller 54K is kept constant. As a fine adjustment, the rotation speed of the anilox roller is finely adjusted so that the image density becomes constant. The image density is kept constant with reference to the patch on the intermediate transfer belt 70.

  The toner regulating blade 52K includes a rubber portion made of urethane rubber or the like that contacts the surface of the toner supply roller 51K and a metal plate that supports the outer rubber portion, and scrapes off the liquid developer remaining on the toner supply roller 51K. Drop and remove.

  The developing roller 54K is a cylindrical member, and rotates counterclockwise around the central axis as shown in FIG. The developing roller 54K is provided with an elastic body such as conductive urethane rubber, a resin layer, and a rubber layer on the outer periphery of an inner core made of metal such as iron. The developing roller 54K is provided with a developing roller blade 58K and a developing roller cleaning liquid recovery unit 59K. The developing roller blade 58K is made of rubber or the like that contacts the surface of the developing roller 54K, and scrapes and removes the liquid developer remaining on the developing roller 54K. The developing roller cleaning liquid recovery unit 59K is a container that stores the liquid developer scraped off by the developing roller blade 58K. The recovered liquid developer in the developing roller cleaning liquid recovery unit 59K is reused.

3A, 3B, 3C, and 3D show examples of the types of compression members that are disposed to face the developing roller 54K. 3A shows a roller type that contacts the developing roller 54K, FIG. 3B shows a roller type that does not contact the developing roller 54K, and FIG. 3C shows a corona discharge type. FIG. 3D shows a conductive blade type in contact with the developing roller 54K. As the type of the compression member, any one of the above is selected and used.
In the following description, the compression roller 55K that contacts the developing roller 54K is used as the compression member.

  The compression roller 55K is a cylindrical member, rotates around the central axis, and includes a conductive resin or rubber layer on the surface layer of the metal roller. As shown in FIG. 2, the rotation direction is clockwise in the direction opposite to the developing roller 54K. A voltage is applied to the compression roller 55K from a voltage application member different from the developing roller 54K, and a potential difference is provided between the two rollers. The compression roller blade 56K is made of rubber or the like that contacts the surface of the compression roller 55K, and scrapes off and removes the liquid developer remaining on the compression roller 55K. The compression roller cleaning liquid recovery unit 57K is a container for storing the liquid developer scraped off by the compression roller blade 56K.

  The photoconductor 20K is a cylindrical member that is wider than the developing roller 54K and has a photosensitive layer formed on the outer peripheral surface thereof, and rotates clockwise around the central axis as shown in FIG. The photosensitive layer of the photoreceptor 20K is composed of an organic photoreceptor or an amorphous silicon photoreceptor.

  The charger 30K is provided upstream of the nip portion between the photoconductor 20K and the developing roller 54K. The charger 30K is applied with a bias having the same polarity as the liquid developer from a power supply device (not shown), and charges the photoconductor 20K. The charged photoconductor 20K is irradiated with laser from the exposure unit 40K to form a latent image. The formed latent image is developed by the developing roller 54K and is primarily transferred to the intermediate transfer belt 70 in the primary transfer unit 60K.

  Next, the operation of such an image forming apparatus will be described. Subsequently, the developing unit will be described by taking the developing unit 50K of the four developing units as an example.

  The liquid developer in the developing toner container 53K has a solid content concentration of 25%, a viscosity of 30 to 10,000 mPa · s, and the toner particles have a positive charge. The liquid developer is pumped up from the developing toner container 53K as the toner supply roller 51K rotates. The toner regulating blade 52K contacts the surface of the toner supply roller 51K, leaves the developer in the groove formed on the surface of the toner toner supply roller 51K, scrapes off other excess developer, and supplies the developer to the development roller 54K. The amount of liquid developer to be controlled is regulated. By this regulation, the film thickness of the liquid developer applied to the developing roller 54K is quantified so as to be 6 μm. The liquid developer scraped off by the toner regulating blade 52K falls into the developing toner container 53K due to gravity.

  The developing roller 54K coated with the liquid developer contacts the compression roller 55K downstream of the nip portion with the toner supply roller 51K. A constant voltage of +300 to +500 V, which is constant voltage controlled by the developing roller voltage applying means 101K, is applied to the developing roller 54K. A voltage equal to or higher than that of the developing roller 54K is applied to the toner supply roller 51K from the same voltage applying unit as that of the developing roller 54K. A voltage higher than the voltage applied to the developing roller by the compression member voltage applying unit 102K different from the developing roller voltage applying unit 101K of the developing roller 54K is applied to the compression roller 55K. Therefore, when the toner on the developing roller 54K passes through the nip with the compression roller 55K, the toner moves to the developing roller 54K side, and only the carrier liquid containing almost no toner particles is collected in the compression roller 55K. As a result, the toner particles are gently coupled to form a film. As a result, the toner moves quickly in the developing unit, and the image density is improved.

  The compression roller 55K rotates in the follower direction at a constant speed with respect to the surface of the developing roller 54K. However, the rotational speed and direction of the compression roller 55K may be different from the rotational speed of the developing roller 54K, or may be rotated in the counter direction facing the surface of the developing roller 54K. The compression roller blade 56K contacts the compression roller 55K. However, the compression roller blade 56K may not be provided. In this case, the carrier having a constant film thickness is held on the compression roller 55K, and the carrier amount of the toner layer on the developing roller 54K does not change before and after the nip with the compression roller 55K.

  The photoreceptor 20K uses amorphous silicon, and charges the surface to about +600 V by applying about +5.5 kV to the wire of the corona charger 30K upstream of the nip portion with the developing roller 54K. After charging, a latent image is formed by the exposure unit 40K so that the potential of the image portion becomes + 25V. In the developing nip portion formed between the developing roller 54K and the photoconductor 20K, a bias + 300V applied to the developing roller 54K and a latent image (image portion + 25V, non-image portion + 600V) on the photoconductor 20K are formed. According to the electric field, the toner particles selectively move to the image portion on the photoconductor 20K. Thereby, a toner image is formed on the photoconductor 20K. Since the carrier liquid is not affected by the electric field, it is separated at the exit of the developing nip between the developing roller 54K and the photoconductor 20K, and adheres to both the developing roller 54K and the photoconductor 20K.

  The photosensitive member 20K that has passed through the developing nip portion passes through the nip portion with the intermediate transfer belt 70, and primary transfer is performed. The primary transfer backup roller 61K is applied with a voltage of about −200 V having a polarity opposite to the charging characteristics of the toner particles by the primary transfer voltage applying means 103K, and the toner particles on the photoconductor 20K are primarily applied to the intermediate transfer belt 70. After the transfer, only the carrier liquid remains on the photoconductor 20K. The carrier liquid remaining on the photoconductor 20K is scraped off by the photoconductor blade 21K downstream of the primary transfer unit and collected by the photoconductor cleaning liquid collection unit 22K.

  The toner image primarily transferred onto the intermediate transfer belt 70 by the primary transfer unit 60K is directed to the secondary transfer unit 80. In the secondary transfer unit 80, a voltage of −1000 V is applied to the secondary transfer roller 81, and the intermediate transfer belt drive roller 82 is maintained at 0 V. The toner particles on the intermediate transfer belt 70 are paper or the like. Secondary transferred to a recording medium.

  While the operation of such an image forming apparatus is continued, a favorable film formation state cannot be obtained, and development / transfer efficiency may change or image distortion may occur. As described above, as described above, regarding the change in the film formation state, it is considered that the compression state fluctuates due to the difference in characteristics between lots of the liquid developer and the change in charging property and movement characteristics of the liquid developer due to the change with time. Further, the change in the film state of the liquid developer may be influenced by the change in the resistance of the developing roller 54K over time or the change in the state of the compression member. That is, when the compression roller 55K of the type that contacts the developing roller 54K is used, a change in effective voltage due to a change in the electrical resistance value of the member is predicted. In addition, when a compression member using corona or micro discharge is used, a change in the discharge state due to the temperature and humidity environment is expected when an electric field is formed by applying an electric charge to the toner. These fluctuations may cause fluctuations in the compressed state of the toner. Changes in the compressed state of the toner may include changes in image density, disturbance of vertical stripes called ribs, and fogging on non-image areas. Cause a malfunction.

  When over-compression of the developer on the developing roller 54K is observed, a phenomenon in which a larger developing current flows between the developing roller 54K and the photoconductor 20K is observed. This is presumed to have the following reasons. When the electric field is applied by the compression member, the toner particles are charged, and it is presumed that the stronger the electric field, the larger the charge amount. Further, when charged particles are dropped onto the toner by a corona or microdischarge is performed by a non-contact type compression roller, it is estimated that the toner charge amount is increased by these charges in addition to the electric field.

  Therefore, the present invention measures the developing current flowing from the developing roller 54K to the photoconductor 20K when forming a solid image, and controls the strength of the electric field applied to the compression member so that the developing current value becomes a specified value. It is. In addition, the charge amount of the toner depending on the compression state has a slightly different value for each color toner. This is presumably because the toner charging characteristics and the resulting toner mobility differ depending on the polarity of the pigment. FIG. 4 is a diagram for explaining development current measurement. In FIG. 4, the compression member is a compression roller 55K that contacts the developing roller 54K.

Preconditions for measuring the development current are the following (1) to (3).
(1) The amount of toner on the developing roller 54K is kept constant. This is realized by transferring the liquid developer quantified by the anilox roller to the developing roller. Further, as the fine adjustment, the rotation speed of the anilox roller is finely adjusted so that the image density becomes constant. The image density is kept constant with reference to the patch on the intermediate transfer belt 70.
(2) The toner solid content concentration in the developing unit is kept constant. When the toner and carrier liquid collected by the developing roller blade 58K, the photoreceptor blade 22K, and other cleaners are reused, the solid content concentration of the collected liquid is different from the solid content concentration of the liquid developer in the developing machine. Then, the solid content concentration is adjusted in the concentration adjusting tank, and the resultant is put into the developing unit.
(3) The development bias voltage is constant.

The development current value measurement sequence is performed during a non-printing operation. The development current measurement sequence is as follows (1) to (7).
(1) When measuring the development current, each roller and the intermediate transfer belt 70 are driven at a normal speed.
(2) At the same time, a developing bias (for example, +300 V) is applied by the developing roller voltage applying unit 101K, and a compressing member bias (for example, +700) is applied by the compressing member voltage applying unit 102K.
(3) At this time, the photosensitive member 20K is not charged, and the primary transfer bias by the primary transfer voltage applying unit 103K is not applied.
(4) Since a solid image is formed on the photoreceptor 20K, at this time, the developing current flowing in the current measuring means 104K in FIG. 4 is measured.
(5) Since the photoconductor 20K is not charged and no primary transfer bias is applied, no current flows from the photoconductor 20K to the intermediate transfer belt 70. Therefore, the current measured by the current measuring means 104K is equal to the developing current flowing from the developing roller 54K to the photoconductor 20K.
(6) After measuring for a certain time, stop the current measurement sequence.
(7) An average current value in the current measurement sequence is obtained, and if it differs from the specified value, the voltage applied to the compression roller 55K is changed and the current measurement sequence is performed. The specified values have different values for each color, and the specified values for each color are shown in Table 1 below.

  If the measured current value is smaller than the specified value, the applied voltage applied to the compression member is increased. Conversely, if the measured current value is larger than the specified value, the applied voltage applied to the compression member is decreased. When the compression member is corona, the wire voltage is adjusted.

  In the case of a color image forming apparatus, the development current measurement sequence can be performed simultaneously for four colors. In addition, when the development current measurement sequence for only some colors is performed, the other developing machines and photoconductors are not driven, and the developing machines and photoconductors are driven for some colors.

It is a figure which shows embodiment of this invention. It is a figure which shows embodiment of this invention. It is a figure which shows embodiment of this invention. It is a figure which shows embodiment of this invention.

Explanation of symbols

20Y, 20M, 20C, 20K: photoconductor, 21K: photoconductor blade, 22K: photoconductor cleaning liquid recovery unit, 30Y, 30M, 30C, 30K: corona charger, 40Y, 40
M, 40C, 40K: exposure unit, 50Y, 50M, 50C, 50K: development unit,
51Y, 51M, 51C, 51K: toner supply roller, 52K: toner regulating blade, 53Y, 53M, 53C, 53K: development toner container, 54Y, 54M, 54C, 54K: development roller, 55K: compression roller, 56K: compression roller Blade, 57K: Compression roller cleaning recovery unit, 58K: Development roller blade, 59K: Development roller cleaning liquid recovery unit, 60Y, 60M, 60C, 60K: Primary transfer unit, 61Y, 61M, 61C, 61K: Primary transfer backup roller, 70: intermediate transfer belt, 80: secondary transfer unit, 81: secondary transfer roller, 82: belt drive roller, 83: secondary transfer roller blade, 84: secondary transfer roller cleaning liquid recovery section, 85: driven roller, 101K: developing roller voltage application means, 102K: compression unit Voltage applying means, 103K: a primary transfer voltage applying means, 104K: current measuring means

Claims (7)

Using a liquid developer in which toner particles are dispersed in a carrier liquid, a developing roller to which a liquid developer quantified by a toner supply roller and a regulating blade is transferred, a compression member disposed opposite to the developing roller, A photosensitive member on which an electrostatic latent image is developed by the developing roller, and the compression member has a function of compressing a solid content toward the developing roller by applying an electric field to the liquid developer on the developing roller; The developing current flowing through the developing roller and the photosensitive member when a predetermined image is formed is measured, and the strength of the electric field applied to the compression member is controlled so that the measurement result becomes a specified value. An image forming method using a liquid developer. The image forming method using a liquid developer according to claim 1, wherein the predetermined image is a solid image. 3. The compression member according to claim 1, wherein the compression member is one of a contact roller type, a non-contact roller type, a type using corona discharge, and a type using a contact type conductive blade. An image forming method using the liquid developer. 4. The image forming method using a liquid developer according to claim 1, wherein in color image formation, a predetermined value of the development current is provided for each of a plurality of colors. The image forming method using the liquid developer according to claim 1, wherein the developing bias voltage is controlled at a constant voltage. 6. The liquid developer according to claim 1, further comprising a concentration adjusting unit that adjusts a solid content concentration in the liquid developer to be constant when the liquid developer is recovered and reused. An image forming method using an agent. Using a liquid developer in which toner particles are dispersed in a carrier liquid, a developing roller to which a liquid developer quantified by a toner supply roller and a regulating blade is transferred, a compression member disposed opposite to the developing roller, A photosensitive member on which an electrostatic latent image is developed by the developing roller, and the compression member has a function of compressing a solid content toward the developing roller by applying an electric field to the liquid developer on the developing roller; Control means for controlling the intensity of the electric field applied to the compression member so as to measure the developing current flowing through the developing roller and the photosensitive member when a predetermined image is formed, and the measurement result becomes a specified value. An image forming apparatus using a liquid developer.

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